Current limiter



V. A. SANDER CURRENT LIMITER Nov. 25, 1952 Original Filed Nov. 28, 1949VW JMOli/L,

Patented Nov. 25, 1952 UNITED STATES PATENT OFFICE CURRENT LIMITERVernon A. Sander, St. Louis, Mo., assignor to W. N. MatthewsCorporation, St. Louis, Mo., a corporation of Missouri 13 Claims.

This invention relates to current limiters and more particularly tothermostatic current limiters for use in a power distribution system tolimit the amount of current drawn by an individual consumer.

This application is a division of my copending application Serial No.129,810, filed November 28, 1949, which has resulted in Patent No.2,565,631 dated August 28, 1951.

This invention is an improvement upon the current limiter disclosed inthe patent of Carl E. Mosley, No. 2,518,361, issued August 8, 1950 andits division, Serial No. 129,775, filed November 28, 1949.

The object of the invention is the provision of an improved, simplified,reliable current limiter of the general type shown in theabove-identified Mosley patent and application which is particularlyadapted for use in three-wire distribution systems for limiting theamount of current drawn by an individual consumer, i. e., to impose apeak limit upon the current which a consumer may use. The currentlimiter is particularly useful for automatically disconnecting asecondary or dispensable load element, such as an electric water heater,if the total load drawn by the consumer should exceed the peak limit. Aconsumer may have, for example, primary load elements such as lights, anelectric range, and other electric appliances, and a dispensable orsecondary load element, such as an electric water heater, all drawingcurrent from a three-wire supply system. With the present invention, theheater, operation of which may be most conveniently discontinued asregards the other load elements, may be connected to draw current at thefull voltage across the outer conductors of the system as long as thetotal load on one leg of the system does not exceed the peak limit,automatically disconnected whenever the total load exceeds the peaklimit, and automatically restored to service when the load drops belowthe peak limit.

In general, a current limiter of this invention comprises a pair ofterminal elements, and a generally E-shaped thermostatic device having apair of outer thermostatic legs adapted to be heated in response to flowof current therethrough and joined at one of their ends by anelectrically conductive connecting member, and having a centralthermostatic leg which is electrically and thermally insulated from theconnecting member extending from the connecting member between the outerlegs. The latter are fixed at their other ends to the terminal elementsand cantilevered outward from the terminal elements so that theconnecting member is free to move as the outer legs flex in response totemperature change. A switch is located adjacent to and is actuated bythe free end of the central leg. With this arrangement, the currentlimiter may be connected in a power consumers wiring system of thisinvention supplied by a three-wire single-phase service to disconnect asecondary appliance, such as a water heater, if the current drawn by theconsumer exceeds a peak limit, without disconnecting the consumers moreessential primary load elements such as lights and an electric range.Other features will be in part apparent and in part pointed outhereinafter.

The invention accordingly comprises the elements and combinations ofelements, features of construction, and arrangements of parts which willbe exemplified in the structures hereinafter described, and the scope ofthe application of which will be indicated in the following claims.

In the accompanying drawing, in which one of various possibleembodiments of the invention is illustrated,

Fig. 1 is a view in side elevation of a current limiter of thisinvention;

Fig. 2 is an end elevation of Fig. 1 as viewed from the right;

Fig. 3 is a plan view of Fig. 1;

Fig. 4 is an enlarged fragmentary section taken on line 44 of Fig. 3;and,

Fig. 5 is a wiring diagram illustrating a mode of connecting the currentlimiter shown in Figs. 1 to 4 in a consumers circuit.

Similar reference characters indicate corresponding parts throughout theseveral views of the drawing.

Referring to the drawing, a current limiter of this invention is shownto comprise a base I consisting of a circular metal plate. This carriesthree main terminals 3, 5 and 1. Each of these main terminals is fixedin an insulation bushing 9 secured in an aperture in the plate toinsulate the terminals from the plate. Each main terminal, asillustrated consists of a flat metal strip, and each bushing has anarrow rectangular opening ll receiving its respective strip, with thestrips extending above and below the plate. At I3 is shown an insulationpanel mounted on and above the base I by means of posts [5 and H. Thepost 15 is a conductor to serve as a terminal and is bolted to the upperend of the terminal 3 as indicated at H]. The post I5 is formed with astep 2| on which the panel 13 bears, the panel being bolted on the stepas indicated at 23. The post l5 extends upward from the step above thepanel through a slot 25 in the panel, and is formed with an outwardlyprojecting ear 2? at its upper end. The post ll does not carry current.

At 29 is shown a conductive terminal post which extends upward from thepanel (3 parallel to the post I5. The post 29 is secured. at its lowerend to the panel as indicated at 31 and has an outwardly projecting ear33 at its upper end at the level of the ear 2! on the upper end of thepost l5. Current-heated thermostatic blades 35 and 3! of compositethermostat metal are secured at one end upon the ears 2'! and 33,respectively, as by welding, and are cantilevered outward in the samedirection from the ears in coplanar, laterally spaced, parallelrelation. The two blades are of substantially the same length and havesubstantially the same temperaturedisplacement characteristics. Eachblade is arranged to bend up upon heating, down upon cooling. Forexample, the blades may be bimetallic with their low coefiicient ofthermal expansion sides on top.

The free ends of the blades are connected by a relatively thickconductive connecting member or bridge 39. This comprises a rigid barbent to have a U-shaped central portion M with flanges 43 extendingoutward from the ends of the arms of the U. The flanges 43 are securedto the upper sides of the free ends of the blades as by welding with theU-shaped central portion opening downward. A block of thermal (andelectrical) insulation 45 is secured "within the U by means of bolts 41.Member 39 is free to move up upon heating of blades 35 and 31, down uponcooling.

A snap-acting switch 49 is mounted on the panel l3 between the posts land '29. This switch is of a type which is conventional in the art,having an insulation case 5! housing the switch contacts and thesnap-acting switchactuating mechanism, and having an operating button 53(Fig. 4) projecting and biased upward through an opening in the top ofthe switchcase. It also has a resilient lever 55 fixed at one end to thetop of the case as indicated at 51 and extending over the button. Thelever 55 is normally raised and may be pushed downward against itsinherent bias to push in the button and open the switch, the switchbeing normally closed. When the lever is raised, the button moves upwardand the switch re-closes.

The switch is held upon the panel [3 between conductive switch-holdingmembers 59 and El secured to the panel to extend along the sides of theswitch case. The member 59 has a portion 63 which reaches through theslot 25 in the panel and which is held in place by the bolt 23 holdingthe panel on the step 2!. This also serves electrically to connect thepost 15 and the member 59. The member'59 also has a portion 55 reachingunder the switch case which is connected to one terminal 66 of theswitch. The member 6! is fastened to the panel at B1 and has a portion69 reaching under the switch case which is connected to the otherterminal iii of the switch. The switch case is held in place between themembers 59 and 6! by means of pins H extending from the case throughholes in the members.

A thermostatic blade element 13 of composite thermostat metal is pivotedat 15 to the insulation block 55 carried by the member 39 and extendsfrom the pivot under the block and centrally between the blades 35 and37. The blade 13 carries a finger H at its free end which bears on theswitch-actuating lever 55. The blade 13 bottom of the block 45 by a bolt80, the pivotal axis being transverse to the center line between theblades 35 and 31. The blade 73 is arranged so that its free end carryingfinger Tl moves upward on heating, downward on cooling. For example, theblade 73 may be a bimetallic blade with its low coeificient of thermalexpansion side on top. As illustrated, the blade 13 is shorter than theblades 35 and 3! but app a e y equal to the length of the blades 35 and31 between the rigid flanges 53 and posts I5 and 29, and it is madethicker than blades 35 and 3?.

The finger l! on the free end of the blade 13 is adapted to bemaintained in pressure engagement with the operating lever 55 of switch9 by means of a screw 8| threaded in an ear 83 formed on the member 35,the screw being located between the pivot 15 and the free end of theblade 13 near the pivot. The screw has a tip 85 of thermal insulationbearing against the upper side of the blade 73. Adjacent its upper end,the screw has a flange 81 (Fig. 4). Bearing against the top of thisflange is a head 89 and bearing against the bottom of the flange is astop disc 9| larger than the head having a notch 93 in its periphery(Fig. 3). The head and disc are tied together by screws 95, whichreleasably clamp them against the flange so that, by loosening thescrews 95, the angular position of the head and disc on the screw 9| maybe varied. A stop pin 91 extends upward from the member 33 through thenotch 93 to limit the rotation of the screw to the arcuate extent of thenotch. It will be seen that the pressure of the finger T! on the lever55 may be varied by turning the screw 3| to move it up or down.

The main terminal 5 is electrically connected to the terminal post 29 bymeans of a conductive rod 99. The main terminal I is electricallyconnected to the member Si by means of a conductive rod NH. The mainterminal 3, as previously described, is directly connected to theterminal post I5.

The blades 35 and 31, the connectin member 39 and. the blade 75 form agenerally E-shaped thermostatic device having its outer currentcarryinglegs 35 and 37 joined at one of their ends by the electricallyconductive connecting member 39 and its central thermostatic leg 13extending from the connecting member 39 between the outer legs, andthermally insulated from the member 39 by the block 45. The outer legsare fixed at their outer ends to the posts I5 and 29, which formterminal elements, and are cantilevered outward from the terminal postsl5 and 29 so that the connecting member is freely movable in response totemperature change as the outer legs 35 and 3? flex. As hereinillustrated in Fig. 4, the connecting member 39 moves up and anglescounter-clockwise when legs 35 and 3? are heated and flex. The blade 73functions as a crank and translates the angling movement of theconnecting member 39 to switch-actuating pressure on the lever 55.

Fig. 5 illustrates a circuit arrangement wherein the above-describedcurrent limiter is con nected in a three-wire single-phase systemsupplying a consumers load requirements shown as including an electricrange R, an electric water heater H, lights and other load elements L.The supply circuit is shown at S, with the neutral Wire of the circuitshown as a dotted line. At M is shown the usual main electric meter,from which lead outer conductors I93 and I05 and a neutral wire I01, thelatter being shown as a dotted line. The conductor I03 is connected tothe terminal 3 of the current limiter. A conductor I09 is connected tothe terminal 5 of the current limiter. The range R is connected acrossconductors Hi5 and I69 and grounded by the neutral wire IB'I. The heaterH is connected across conductors I 63 and [15 in a circuit including theswitch 49 by means of a wire III connected to one terminal of the heaterand to the terminal l of the current limiter and a wire H3 connected tothe other terminal of the heater and to the wire I05 at I IS. The heateris grounded by a neutral wire III connected to the neutral wire It)! atI I9. The load elements L are connected in two separate circuits I2! andH3, one being connected across conductor I99 and neutral wire It? andthe other across conductor H35 and neutral wire I01.

In operation, current flows in series through thermostatic element 35,member 39 and thermostatic element 31 or" the E-shaped thermostaticdevice. The thermostatic elements 35 and 31 are thereby heated to adegree dependent upon the current value. The value of the currentflowing through the thermostatic device is dependent upon the loadimposed by the range R and the load elements L. Whenever the currentdrawn by the range and load element-s L exceeds a predetermined peakvalue, as determined by the setting of the screw SI, the thermostaticelements 35 and 31 are heated to such an extent that the member 39angles in one direction and acts through the plate I3 to open the switch49, thereby disconnecting the water heater H. When the current dropsbelow the peak value, the elements 35 and 31 cool, member 39 angles inthe other direction, and permits the switch 59 to re-connect the heaterH. The arrangement is such that the customer may, if desired,voluntarily reduce the load imposed by the range R or the load elementsL below the peak value to maintain the heater connected.

The peak value may be varied within limits by varying the adjustment ofthe screw 8! By adjusting the screw downward, thereby increasing thepressure of the finger H on the switch lever 55, the peak value may bereduced, and by adjusting the screw upward, the peak value may beraised. Suitable indicia indicating the peak values that may be set maybe scribed on the head 89 and read in conjunction with pin 91 as anindex.

As shown in Fig. 5, the heater H is connected in the circuit ahead ofthe current limiter, and the current drawn by the heater has no efiecton the current limiter. If desired, the heater I-l may be connected sothat the current drawn thereby iiows through the thermostatic device ofthe current limiter simply by reversing the connections of conductorsI83 and I98, 1. e., connecting conductor I83 to terminal 5 andconnecting conductor Ills to terminal 3.

The central thermostatic leg '53 of the E- shaped thermostatic devicedoes not carry current, being electrically as well as thermallyinsulated from the member 38 by the insulation block 45. This thermalinsulation of the leg '53 from the member 39 is important because itprevents leg lt from being heated by conduction and changing theoperating characteristics. The central leg '53 acts as aswitch-operating arm and is made thermostatic to afford ambienttemperature compensation by reason of the fact that as member 39 movesin response to ambient temperature changes, the end of the leg 73 movesin such direction as to counteract the movement of the member 39. Forexample, if the ambient temperature increases and member 39 moves upwardin switch-opening direction, the free end of leg I3 moves upward tooffset the tendency of member 39 to open the switch. The leg 13 is madethicker than the legs 35 and 31 as it bears a greater mechanical loadand its length is made such as to aiTord the necessary deflection of itsfree end for ambient temperature compensation. The hinging of the leg I3to the member 39 is an important feature as it has the advantage ofeliminating the effect of any difierence between theternperature-displacement characteristics of legs 35 and 3?.

In View of the above, it will be seen that the several objects or" theinvention are achieved and other advantageous results attained.

As many changes could be made in the above construction withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description r shown in the accompanyingdrawing shall be interpreted as illustrative and not in a limitingsense.

I claim:

1. A current limiter comprising a pair of terminal elements, a generallyE-shaped thermostatic device having a pair of outer thermostatic legs ofcomposite thermostat metal adapted to be heated in response to flow ofcurrent there through and joined at one of their ends by an electricallyconductive connecting member, and having a central leg which iselectrically and thermally insulated from the connecting memberextending from the connecting member between the outer legs, the outerlegs being fixed at their other ends to the terminal elements andcantilevered outward therefrom so that the connecting member is free tomove as the outer legs flex in response to temperature change, and aswitch located adjacent to and actuated by the free end of the centralleg, said central leg comprising a thermostatic element of compositethermostat metal arranged for movement of its free end in the samedirection as the connecting member in response to ambient temperaturechange, the connecting member being angled by flexing of said outer legsand the central leg being angled by the connecting member.

2. A current limiter comprising a pair of terminal elements, a generallyE-shaped thermostatic device having a pair of outer thermostatic legs ofcomposite thermostat metal adapted to be heated in response to flow ofcurrent therethrough and joined at one of their ends by an electricallyconductive connecting member, and having a central leg which iselectrically and thermally insulated from the connecting memberextending from the connecting member b tween the outer legs, the outerlegs being fixed at their other ends to the terminal elements andcantilevered outward therefrom so that the connecting member is free tomove as the outer legs flex in response to temperature change, and asnap-acting switch comprising a case housing the switch contacts andhaving an operating button projecting from the case located foractuation of the button by the free end of the central leg, said centralleg comprising a thermostatic element of composite thermostat metalarranged for movement of its free end in the same direction as theconnecting member in response to ambient temperature change, theconnecting member being angled by flexing of said outer "legs and saidcentral "leg being angled by the connecting member.

3. A current limiter comprising a support, a pair of rigid terminalposts mounted upon the support, .a generally E-shaped thermostaticdevice having an outer pair of relatively flexible :blades each fixed atone end to a terminal post and :arranged in generally coplanar laterallyspaced parallel relation, a relatively rigid conductive connectingmember joining the .other and free ends of said blades and providing ,anelectric circuit for electric heating thereof; a normally-closedsnap-acting switch mounted upon said support between the terminal posts,said switch having an operating element biased away from the .supportand movable toward the support to actuate the switch; and a centralthermostatic blade attached at one end'to the connecting member by meanswhich thermally insulates the central blade from the connecting member,the other end of the central blade bearing against the switch-operatingelement; the outer blades being formed of composite thermostatic metalarranged so that they flex generally away from the support when heated,thereby angling the central thermostatic blade toward the support toactuate the switch, and the central blade being formed of compositethermostat metal arranged to flex in the same direction as the outerblades in response to ambient temperature changes.

4. A current limiter as set forth in claim 3, wherein the connectingmember is arched, and a block of thermal insulation is fixed in the archof said connecting member, said central thermostatic blade being mountedon the block of thermal insulation so as to extend normally insubstantially coplanar relation with the outer thermostatic blades.

5. A current limiter as set forth in claim wherein the centralthermostatic blade is mounted upon the block of thermal insulation bymeans of metal studs and the block is mounted upon the connecting memberby other metal studs.

6. A current limiter as set forth in claim 3 wherein the connectingmember has an ear extending over the central thermostatic blade, throughwhich is threaded a screw that bears against the central thermostaticblade and which is adjustable for varying the pressure of the centralblade on the switch-operating element.

'7. A current limiter as set forth in claim 6 wherein the tip of thescrew bearing against the central thermostatic blade is formed ofthermal insulation.

8. A current limiter comprising an insulation support, a pair ofterminal. posts on the support, a pair of normally generally fiatcurrent-heated thermostatic blades of composite thermostat metal, onefixed at one end to one post and the other fixed at one end to the otherpost, the blades extending outward from the posts as cantilevers ingenerally coplanar laterally spaced parallel relation, an electricallyconductive bridge joining the free ends of the blades and movable by theblades as the latter flex in response to the same direction as thebridge in response 'to ambient temperature change, a snap-acting switchon the support having a switch-operating element engaged by the free endof the operating arm, and an adjusting member carried by the bridgeengaging the arm for causing the arm to bear upon the switch-operatingelement and adjustable relative to the bridge for varying the pressureof the arm on the switch-operating element.

9. A current limiter as set ,forth in claim 8 wherein the bridge has ablock of thermal insulating material fixed thereto, wherein theoperating arm is pivotally'connected to said block, and wherein theadjusting member engages one side of the operating arm between itspivotal connection to the block and its free end and theswitch-operating element is in engagement with the other side of the armadjacent its free end.

10. A current limiter as set forth in claim 9 wherein the adjustingmember comprises ascrew threaded in the bridge and having a thermalinsulation tip bearing against the arm.

11. A current limiter as set forth in claim 9 wherein the adjustingmember comprises a screw threaded in the bridge and having a thermalinsulation tip bearing against the arm, wherein the screw carries a stopdisc having a notch :in its periphery, and wherein a pin extends fromthe bridge through the notch.

12. A current limiter comprising an insulation support, a pair ofnormally generally flat current-heatable thermostatic blades ofcomposite thermostat metal, each fixed at one end to the support andextending as a cantilever from the support with its other end free ofthe support, the blades being positioned in generally coplanar laterallyspaced side-by-side relation and arranged so that both flex in onedirection in unison upon increase in temperature and in the oppositedirection upon decrease in temperature, an electrically conductivebridge joining the free ends of the blades and movable by the blades asthe latter fiex in response to temperature change, a third normallygenerally flat thermostatic blade of composite thermostat metalextending from the bridge between the first two blades and electricallyand thermally insulated from the bridge. and arranged to flex in thesame manner as the first two blades in response to ambient temperaturechange, and a switch carried by the support and having aswitch-operating element operable by the free end of said third blade.

13. A current limiter as set forth in claim 12 wherein the switchcomprises a snap-acting switch comprising a case housing switch contactsand having an operating button projecting from the case and positionedfor actuation of the button by the free end of said third blade.

VERNON A. SANDER.

REFERENCES orran The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,849,280 Chandler Mar. 15, 19322,280,960 Lee Apr. 28, 1942 2,284,644 Dubilier June 2, -l9l2 2,302,399Stimson Nov. 17, 1942 2,518,361 Mosley Aug. 8, 1950

